New electronic components are supplied with ever lower voltages (2.5 V, 1.8V, . . . 1.65 V and soon less than 1 V), the power requirements around the very low voltages are increasing and becoming predominant relative to the more conventional voltages +/−15 V et +5 V and 3.3 V.
Voltages below 3.3 V are not distributed and are installed directly onto user cards. The power supply is being moved as close as possible to the users so as to ensure better distribution and regulation.
The currents consumed are becoming ever larger since the power consumed by users is still the same or increasing (more numerous functionalities).
This trend is compelling providers of power supplies to make converters generating ever greater ratios of input voltage to output voltage.
The structures used are generally chopping converters that are not isolated for reasons of complexity, cost and to preserve high efficiencies as well as small dimensions. With a step-down type structure, these converters can with difficulty produce a transformation ratio of greater than 10 with efficiencies of greater than 90%.
To meet the requirements of the market to fulfill its integration demands, it is necessary to be able to provide these new converters in even smaller areas and hence with ever greater efficiencies so as not to increase the size of the dissipaters, and hence the size of the overall function (converters+dissipaters).
Among the structures of converters are step-down series choppers also known as “buck converters”.
FIG. 1a shows the basic diagram of a “buck converter”.
The circuit of FIG. 1a is supplied with a DC input voltage Vin and provides an output voltage Vout on a load R. An input capacitor Cin is present in parallel with the input. When it is operated for a time Ton, a breaker 10 makes it possible to apply the positive potential of the input voltage Vin to a terminal of an inductor L. The other terminal of the inductor is connected to a terminal of the load resistor R. The other terminal of the resistor is connected to the negative potential of the input voltage Vin. It will be assumed subsequently that the negative potential of Vin is 0 volts. When the breaker 10 is not operated for a time Toff, a diode D connected between the common point of the breaker and of the inductor and the negative potential of the input voltage Vin ensures the continuity of the current in the inductor.